The most frequent initial nursing intervention to treat dyspnea in mechanically ventilated patients is tracheal suction, yet research to direct these care decisions has just begun. The purpose of this study is to determine the pattern of dyspnea after tracheal suction, and to determine how well the amount of mucus removed by suctioning, airway resistance, and positive end expiratory pressure predict the reduction in dyspnea. Initial research, dyspnea theory, and clinical practice have directed the selection of dyspnea reduction predictors for this study. Repeated measures design will be used to determine the pattern of dyspnea, with measurements obtained at immediately before suction, immediately after suction, and every 10 minutes until 60 minutes after suctioning. The sample will consist of 40 adult, oriented, mechanically ventilated patients in critical care units of one hospital. Patients must have required tracheal suction every 1-4 hours in the past 8 hours, have a minimum ventilator rate of at least 6 breaths per minute, spontaneously initiated at least 1 breath per minute, be able to see the markings on the visual analogue scale, and have an arterial oxygen saturation of at least 90%. Dyspnea is measured by a visual analogue scale. The amount of mucus removed by suctioning is measured by subtracting the weights of the closed suction system and mucus trap with original packaging before and after suctioning. the patient's airway resistance and positive and expiratory pressure are measured from continuous transducer and pneumotachometer recordings stored in a computer. The suctioning procedure involves hyperoxygenation, normal saline instillation into trachea, and 3 passes of the suction catheter for 10 seconds each at 16 L/min. flow rate. General linear modeling the hierarchial multiple regression will be used for data analysis. Millions of people each year are admitted to intensive care units and most are suctioned every 1 to 2 hours. However, we don't know when and to what extent dyspnea should be relived by suctioning, nor predictors of that outcome. Addressing these questions could prolong life and reduce hospital costs by providing a basis for nursing care decisions regarding suctioning, since dyspnea is associated with mortality and delayed weaning from the ventilators.